1. Field of the Invention
The present invention relates to a colored composition and a photosensitive transfer material for producing a black matrix, a black matrix and a method for producing the same, a color filter, a liquid crystal display, and a black matrix substrate.
2. Description of the Related Art
In color filters used for color liquid crystal displays, red (R), green (G) and blue (B) pixel layers are formed on a transparent substrate, and gaps between the R, G and B pixels are filled with a black matrix for the purpose of improving display contrast or the like. The black matrix must have a high light-shielding property, especially in an active-matrix driving type liquid crystal display using thin-film transistors (TFTs), for the additional purpose of preventing degradation of image quality, which results from leakage of current caused by light from the thin-film transistor.
When, for example, a film of metal such as chromium is used as a light-shielding layer, the black matrix is produced as follows: a thin metal film is produced by a vacuum deposition process or a sputtering process; a photoresist is applied to the thin metal film; the photoresist layer is exposed, by using a photomask having a pattern for the black matrix, and developed; the exposed thin metal film is etched; and the photoresist layer is removed from the thin metal film. (See, for example, pp. 218 to 220 of Color TFT Liquid Crystal Display, published by Kyoritsu Shuppan Co., Ltd., Apr. 10, 1997.)
In this method, since a thin metal film is used, a good light-shielding effect is obtained even when the film is very thin. However, this method requires a vacuum film-formation step, such as the vacuum deposition process or sputtering process, and an etching step, and thus, not only are costs increased but also the impact on the environment cannot be ignored. Further, metal film is highly reflective, and thus, display contrast is low under strong outdoor light. With regard to the latter problem, there is a solution in using a low-reflecting chromium film (e.g., a film comprising a chromium metal layer and a chromium oxide layer), however, this inevitably increases costs even more.
Another method for producing the black matrix involves using a photosensitive resin composition containing a light-shielding pigment such as carbon black. An example of this is a self-alignment type method which involves the following: R, G and B pixels are formed on a transparent substrate; a photosensitive resin composition containing carbon black is applied to the pixels; and the entire surface of the photosensitive resin layer is exposed to light from the side of the transparent substrate on which the R, G and B pixels have not been formed (e.g., Japanese Patent Application Laid-Open (JP-A) No. 62-9301).
In this method, the cost of production is lower than that of the former method of etching a metal film, however, in order to obtain a satisfactory degree of light-shielding, the photosensitive resin layer becomes very thick. As a result, overlap of the black matrix and the R, G and B pixels (i.e., difference in level) is caused, and the flatness of the color filter is thereby degraded. This causes cell-gap unevenness in the liquid crystal display, resulting in a defective display having uneven color or the like.
Japanese Patent No. 3,318,353 describes the following method for producing a black matrix in which light-shielding metal particles each having a particle diameter of 0.01 to 0.05 μm are uniformly dispersed: a photosensitive resist layer containing a hydrophilic resin is formed on a transparent substrate, and is then exposed through a photomask having a pattern for the black matrix, and developed, so as to form a relief on the transparent substrate; the transparent substrate is brought into contact with an aqueous solution of a metal compound serving as a catalyst for electroless plating, such that the relief contains the metal compound; the transparent substrate is dried and subjected to heat treatment; and the relief on the transparent substrate is brought into contact with a solution for electroless plating. For the metal particles, this patent discloses possible use of nickel, cobalt, iron, copper and chromium, and as a specific example thereof, only nickel is shown.
However, this method comprises the above-described overly methodical steps of handling aqueous solutions involving forming a relief, including exposure and development; applying a catalyst for electroless plating; heat treatment; and electroless plating. Accordingly, it is difficult to attain production of the black matrix at low cost.
Further, although Japanese Patent No. 3,318,353 does not describe or mention silver at all, there is another problem in that, when the metal particles are silver particles each having a particle diameter of 0.01 to 0.05 μm, unwanted coloring from yellow to red is caused and a proper black cannot be obtained.
Accordingly, there has been need for a colored composition and a photosensitive transfer material, from which a black matrix, which is a thin film and has high light-shielding performance, can be produced at low cost. There has also been need for both a black matrix produced by using the colored composition and a method for producing the same, a color filter and a liquid crystal display provided with the black matrix. There has also been need for a black matrix substrate, which is a thin film and has high light-shielding performance.